Adjustable Riser Suspension System

ABSTRACT

A riser suspension system for suspending a riser from a subsea wellhead housing using a running tool. The system comprises a surface wellhead housing, a riser hanger and a load shoulder. The surface wellhead housing comprises a bore, a shoulder profile, a lock profile and a support ring. The riser hanger assembly comprises a hanger body, an adjustable suspension mechanism rotationally coupled with the hanger body and a lock ring expandable into engagement with the lock profile. The load shoulder assembly couples with the riser hanger assembly and comprises a lock ring expandable into engagement with the shoulder profile. The invention further claims a multi-function running tool that requires only a single trip and which can manipulate, latch and back up a tie-back adapter into the downhole equipment and provide positive preloaded, locked-in, tension of the riser.

BACKGROUND

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Drilling and producing offshore oil and gas wells includes the use of offshore platforms for the exploitation of subsea petroleum and natural gas deposits. In deep water applications, floating platforms (such as spars, tension leg platforms, extended draft platforms, and semi-submersible platforms) are typically used.

One type of offshore platform, a tension leg platform (“TLP”), is a vertically moored floating structure used for offshore oil and gas production. The TLP is permanently moored by groups of tethers, called tension legs or tendons, that eliminate virtually all vertical motion of the TLP due to wind, waves, and currents. The tension legs are maintained in tension at all times by ensuring net positive TLP buoyancy under all environmental conditions. The tension legs stiffly restrain the TLP against vertical offset, essentially preventing heave, pitch, and roll, yet they compliantly restrain the TLP against lateral offset, allowing limited surge, sway, and yaw.

Another type of platform is a spar, which typically consists of a large-diameter, single vertical cylinder extending into the water and supporting a deck. Spars are moored to the seabed like TLPs, but whereas a TLP has vertical tension tethers, a spar has more conventional mooring lines.

The offshore platform typically supports risers that extend from one or more subsea wellheads or structures on the seabed to one or more production wellheads on the sea surface. The risers connect the subsea well with the platform to protect the fluid integrity of the well and to provide a fluid conduit to and from the wellbore. During drilling operations, a drilling riser is used to maintain fluid integrity of the well. After drilling is completed, a production riser is installed.

The risers that connect the surface wellhead to the subsea wellhead can be thousands of feet long and extremely heavy. To keep the risers as light as possible, they are designed so as to not be able to withstand their own weight, even when in water. In fact, the connectors used to connect sections of some risers are designed to be weaker than the riser sections themselves. An example of such connectors is a thread and couple connector where the ends of two adjacent riser sections are both threaded into the connector. When the riser is placed under conditions exceeding operating limits, the connectors will actually be the first components to fail.

A typical drilling riser comprises two or more concentric tubular risers, with the outermost riser, sometimes referred to herein as a “casing” or “casing riser,” which can be tensioned by hydraulic machines mounted to the surface, and an inner riser. To prevent the risers from buckling under their own weight or placing too much stress on the subsea wellhead, upward tension is applied, or the riser is lifted, to relieve a portion of the weight of the riser. Since offshore platforms are subject to motion due to wind, waves, and currents, the risers must be tensioned so as to permit the platform to move relative to the risers. Accordingly, the tensioning mechanism must exert a substantially continuous tension force to the riser within a well-defined range so as to compensate for the movement of the platform.

A need exists for a riser hanger capable of providing adjustability in length for a riser secured at the lower end from a subsea wellhead while insuring a positive, preloaded, locked-in condition using only a single running tool. This preloaded, locked-in condition is necessary to insure that the riser hanger will not move upward or downward at any time as a result of fluctuating tension loads, temperatures or pressures which may be experienced during either drilling or production scenarios. Limited movement is beneficial for all types of seals which may be used to seal the bore and annulus. It is particularly useful for demanding applications requiring the use of metal-to-metal seals. Successful metal-to-metal seal performance is typically linked directly to the ability to preclude any potential movement that may occur between components to be sealed (e.g., hanger and head). The obstacle to overcome is formidable as a single tool must allow not only selective actions to occur but also permit repositioning as required. The claimed single trip tool is required to support high lift loads as well as deliver high torque.

In accordance with the present invention, only a single running tool is necessary to perform any required function during running, tieback, tensioning, and locking. Although versatile enough for use on surface wells requiring a tension type hanger (i.e., hanger which must travel past respective land-off in the head to perform the lower tieback prior to application of tension and then again during the tensioning process), extreme benefits are realized for offshore use. In deepwater applications, such a device is necessary for safely allowing elevation of working pressure during drilling operations as the hole progresses by simply employing a smaller diameter high pressure inner riser without the need for removal of the low pressure equipment. The claimed invention is a unique and fully secured preloaded support system capable of supporting use of metal seals, which are normally required for demanding use with surface vessels, including TLP and spar platforms.

BRIEF SUMMARY

Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.

In accordance with various embodiments, a riser suspension system for suspending a riser from a subsea wellhead housing using a running tool is disclosed. The system includes a surface wellhead housing, a riser hanger, and a load shoulder. The surface wellhead housing comprises a bore, a shoulder profile, a lock profile, and a support ring. The riser hanger assembly comprises a hanger body, an adjustable suspension mechanism rotationally coupled with the hanger body and a lock ring expandable into engagement with the lock profile.

The load shoulder assembly couples with the riser hanger assembly and comprises a lock ring expandable into engagement with the shoulder profile. The adjustable suspension mechanism is selectively, axially adjustable relative to the load shoulder assembly to support the riser hanger assembly and the riser when engaged with the load shoulder assembly. The invention further claims a multi-function running tool that requires only a single trip to tension the riser, and which can manipulate, latch and back up a riser into the downhole equipment and provide positive preloaded, locked-in, tension of the riser.

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

DRAWINGS

For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:

FIG. 1 shows an offshore sea-based drilling system in accordance with various embodiments;

FIGS. 2-14 show embodiments of the disclosed system for suspending a riser under tension from a subsea wellhead housing using a running tool, the running tool itself, as well as a seal assembly.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis.

Referring now to FIG. 1, a schematic view of an offshore drilling system 10 is shown. Drilling system 10 comprises an offshore drilling platform 11 equipped with a derrick 12 that supports a hoist 13. Drilling of oil and gas wells is carried out by a string of drill pipes connected together by “tool” joints 14 so as to form a drill string 15 extending subsea from platform 11. The hoist 13 suspends a kelly 16 used to lower the drill string 15.

Connected to the lower end of the drill string 15 is a drill bit 17. The bit 17 is rotated by rotating the drill string 15 and/or a downhole motor (e.g., downhole mud motor). Drilling fluid, also referred to as drilling “mud,” is pumped by mud recirculation equipment 18 (e.g., mud pumps, shakers) disposed on platform 11. The drilling mud is pumped at a relatively high pressure and volume through the drilling kelly 16 and down the drill string 15 to the drill bit 17. The drilling mud exits the drill bit 17 through nozzles or jets in face of the drill bit 17. The mud then returns to the platform 11 at the sea surface 21 via an annulus 22 between the drill string 15 and the borehole 23, through subsea wellhead 19 at the sea floor 24, and up an annulus 25 between the drill string 15 and a casing 26 extending through the sea 27 from the subsea wellhead 19 to the platform 11. At the sea surface 21, the drilling mud is cleaned and then recirculated by the recirculation equipment 18. The drilling mud is used to cool the drill bit 17, to carry cuttings from the base of the borehole to the platform 11, and to balance the hydrostatic pressure in the rock formations.

As illustrated in FIG. 1, the casing 26 is coupled to the surface wellhead assembly and held under tension to prevent buckling and reduce the load on the subsea wellhead 200. An adapter spool 201 is coupled to the wellhead housing 200. As illustrated in FIG. 2, the surface wellhead housing 200 comprises a bore 202, a shoulder profile 203, and a lock profile 204. In the example shown, the surface wellhead housing 200 can be landed on top of a tension joint 206. However, it should be appreciated that the surface wellhead assembly 200 may be located in any suitable location for supporting a riser.

As illustrated in FIG. 3, a riser hanger assembly 300 is run into the wellhead housing 200 by way of the running tool 301 and lowered below a land-off point 302 and connected with the subsea wellhead 200 such that a lower end of the riser 310 is locked with the subsea wellhead 200. The riser hanger assembly 300 comprises a riser hanger body to support the riser, an adjustable load shoulder 303 rotationally coupled with the hanger body, and a lock ring 304 expandable into engagement with the lock profile 204 to lock the riser hanger assembly 300 into a locked position.

As illustrated in FIGS. 4-6, lock pins 400 are provided which are configured to be run into the riser hanger assembly 300, thereby energizing a snap ring 401. When energized, the snap ring 401 engages with the load shoulder assembly 202. The lock pins 400 are one example of an actuation mechanism for the snap ring 401. The lock pins 400 can be activated by any means known to those of ordinary skill in the art, including hydraulically or manually. After installing the lower end of the riser 310 with the subsea wellhead 200, the riser hanger assembly 300 and riser 310 are then pulled up such that a load shoulder assembly 402 releasably engaged with the riser hanger assembly 300 is raised above the land-off point 302. The riser hanger assembly 300 has a greater outer diameter than the snap ring 401 inner diameter in the extended position and is, therefore, restricted from moving down lower than the snap ring 401. This allows force to be applied to the load shoulder assembly 402 from the riser hanger assembly 300, which releases the load shoulder assembly 402 from the riser hanger assembly 300. For example, moving the riser hanger assembly 300 lower in the wellhead housing 200 may shear shearing pins and release the load shoulder assembly 402, allowing the riser hanger assembly 300 to continue to be lowered relative to the load shoulder assembly 402. Further lowering the riser hanger assembly 300 sets a lock ring 304 of the load shoulder assembly 402 to lock the load shoulder assembly 402 into the shoulder profile 204.

As illustrated in FIG. 7, the load shoulder assembly 402 has been locked to the wellhead housing 200 and is ready to support the riser hanger assembly 300 with the riser 310 in tension. As shown, a worm drive 700 is provided. The worm drive 700 is selectively engageable with a castleated overshot sleeve 701. Applying torque to the worm drive 700 turns the castleated overshot sleeve 701 that lowers the adjustment suspension mechanism as it rotates along a threaded engagement with the outside of the riser hanger body. The adjustment suspension mechanism is lowered until it contacts the load shoulder 402, thus transferring the support load of the riser hanger assembly 300 and riser 310 from the running tool 301 to the load shoulder assembly 402 and the wellhead housing 200.

As illustrated in FIGS. 8-10, pressure can be applied through the drill pipe 800 to disengage the running tool 301 from the riser hanger assembly 300. The running tool 301 can then be raised to reengage with the overshot sleeve 701 profile. As illustrated in FIG. 11, torque can be applied via the running tool 301 to pre-load the lock ring 304 into engagement with the lock profile 204, thereby securing the position of the riser hanger assembly from movement either in or out of the wellhead housing. As illustrated in FIG. 12, the running tool 301 can be disengaged from the assembly after preloading the lock ring 304 and withdrawn from the assembly.

As illustrated in FIGS. 13-14, a seal assembly 1300 can be run into the wellhead assembly 200 comprising upper 1301 and lower 1302 seals. The seals can be made of any material known to those of ordinary skill in the art, including metal and/or elastomers.

The embodiments described above and illustrated in the figures provide for single-trip riser adjustment and tensioning through the bore wherein the running tool is used to manipulate and lock in the riser without having to disengage the running tool from the riser until after the desired riser tension is selected and the riser locked into place. Multiple functions can be performed by the running tool during the single trip through the bore, including preloaded locking of the riser.

While specific embodiments have been shown and described, modifications can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments as described are exemplary only and are not limiting. Many variations and modifications are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. 

What is claimed is:
 1. A system for tying back a riser under tension from a platform to a subsea wellhead housing using a running tool, comprising: a surface wellhead housing comprising a bore; a riser hanger assembly installable in the bore and comprising: a hanger body to support the riser; and an adjustable suspension mechanism coupled with the hanger body; a load shoulder assembly releasably coupled with the riser hanger assembly and comprising a load shoulder, the load shoulder assembly being releasable from the riser hanger assembly and lockable to the wellhead housing inside the bore using force from the riser hanger assembly; and wherein the adjustable suspension mechanism is axially adjustable relative to the hanger body to engage the load shoulder and support the riser hanger with the riser in tension.
 2. The adjustable riser suspension system of claim 1, further comprising: the surface wellhead housing further comprising: a bore wall; and a support ring selectively extendable from a position recessed into the bore wall to an extended position within the bore; and wherein the load shoulder assembly is restricted from movement upon engagement with the support ring in the extended position to allow application of force from the riser hanger assembly.
 3. The adjustable riser suspension system of claim 1, further comprising: the surface wellhead housing further comprising: a bore wall; and a shoulder profile recessed into the bore wall; and the load shoulder assembly comprising a shoulder lock ring expandable into engagement with the shoulder profile to lock the load shoulder assembly to the surface wellhead.
 4. The adjustable riser suspension system of claim 1, further comprising: the surface wellhead housing further comprising: a bore wall; and a lock profile recessed into the bore wall; and the riser hanger assembly further comprising a hanger lock ring expandable into engagement with the lock profile to lock the riser hanger assembly to the surface wellhead.
 5. The adjustable riser suspension system of claim 1, further comprising an overshot sleeve, wherein the running tool rotates the overshot sleeve about the riser hanger to engage the load shoulder assembly into the lock profile.
 6. The adjustable riser suspension system of claim 1, further comprising a seal assembly with upper and lower ends.
 7. The adjustable riser suspension system of claim 6, wherein the seal assembly comprises metal-to-metal seals.
 8. The adjustable riser suspension system of claim 6, wherein the seal assembly comprises elastomeric seals.
 9. The adjustable riser suspension system of claim 1, wherein the riser, load shoulder and hanger are installable in one trip.
 10. A method for tying back a riser under tension from a platform to a subsea wellhead housing, comprising: coupling the riser to a surface wellhead and suspending the riser and a riser hanger assembly inside an outer riser, wherein the riser hanger assembly comprises an adjustable suspension mechanism; lowering the riser hanger assembly downward relative to the riser, causing a lower end of the riser to engage the subsea wellhead; raising the riser hanger assembly upward relative to the riser; lowering the adjustable suspension mechanism relative to the riser to engage with a load shoulder assembly, wherein the adjustable suspension mechanism supports the riser hanger assembly when engaged with the load shoulder assembly.
 11. The method of claim 10, wherein the surface wellhead housing further comprises: a bore wall; and a support ring selectively extendable from a position recessed into the bore wall to an extended position within the bore; and wherein the load shoulder assembly is restricted from movement upon engagement with the support ring in the extended position to allow application of force from the riser hanger assembly.
 12. The method of claim 10, wherein the surface wellhead housing further comprises: a bore wall; and a shoulder profile recessed into the bore wall; and the load shoulder assembly comprising a shoulder lock ring expandable into engagement with the shoulder profile to lock the load shoulder assembly to the surface wellhead.
 13. The method of claim 10, wherein the surface wellhead housing further comprises: a bore wall; and a lock profile recessed into the bore wall; and the riser hanger assembly further comprising a hanger lock ring expandable into engagement with the lock profile to lock the riser hanger assembly to the surface wellhead.
 14. The adjustable riser suspension system of claim 10, further comprising an overshot sleeve, wherein the running tool rotates the overshot sleeve about the riser hanger to engage the load shoulder assembly into the lock profile.
 15. The adjustable riser suspension system of claim 10, further comprising a seal assembly with upper and lower ends.
 16. The adjustable riser suspension system of claim 15, wherein the seal assembly comprises metal-to-metal seals.
 17. The adjustable riser suspension system of claim 15, wherein the seal assembly comprises elastomeric seals.
 18. The adjustable riser suspension system of claim 10, wherein the riser, load shoulder and hanger are installable in one trip. 